Friction design method for sliding parts, surface roughness management method, and manufacturing method of sliding mechanism

Abstract

The friction design method accurately estimates the sliding friction generated on the sliding surfaces of two sliding parts lubricated with a lubricant. The method sets a friction coefficient μ in a sliding surface model corresponding to the sliding surfaces of two sliding parts (2, 3) lubricated with a lubricant (step S1), and sets a target value for the surface roughness of the sliding surface to be managed as a product (steps S3 to S6) based on the correlation between the friction coefficient μ and an oil film parameter (Λ(Rk) or Λ(Rk+Rpk)) calculated using a center level difference (Rk) or the sum of a center level difference (Rk) and a protruding peak height (Rpk) as a parameter representing the surface roughness in the sliding surface model (steps S3 to S6).

Description

Technical Field

[0001] The present invention relates to a friction design method and a surface roughness management method for the sliding surfaces between two sliding parts lubricated with a lubricant (for example, the opposing surfaces between the roller head and the large flange of a tapered roller bearing), and a method for manufacturing a sliding mechanism having such sliding surfaces. Background Art

[0002] Sliding mechanisms comprised of sliding parts that have sliding surfaces and generate sliding friction as they slide include rolling bearings, plain bearings, ball screws, and gears. These sliding mechanisms utilize grease or oil for lubrication between the sliding surfaces of the sliding parts. However, at low operating speeds, a sufficient oil film cannot be formed, resulting in high friction. Therefore, there is a desire to reduce torque in the low operating speed range.

[0003] Among rolling bearings, tapered roller bearings, for example, are used in transmissions, differentials, drive axles, and other locations. While tapered roller bearings offer advantages over other bearings in terms of rigidity and load capacity, they also have the disadvantage of relatively high torque in the low-speed range. In particular, differentials, where the rotational speed is frequently used, often as low as several hundred rpm, tend to exhibit high torque in this low-speed range. Therefore, reducing torque in this low-speed range is desirable.

[0004] The reason why the torque of a tapered roller bearing is high in the low rotation range is that the sliding surfaces between the roller head and the large flange are in rolling sliding contact, and the lubrication state of the sliding surface is boundary lubrication or mixed lubrication with local solid contact.

[0005] That is, by using high-viscosity oil to increase the oil film thickness or reduce the surface roughness of the tapered roller bearing, the lubrication state is changed to fluid lubrication in which the sliding surfaces of the roller head and the large flange are separated by the oil film, thereby reducing friction in the low rotation range.

[0006] However, in recent years, the trend toward lower viscosity lubricants for improved fuel efficiency has led to the widespread use of lubricants with kinematic viscosities of 30 cSt @ 40°C (7 cSt @ 100°C) or less. In the future, further reductions in lubricant viscosity are expected, with lubricants with viscosities of 20 cSt @ 40°C or less expected.

[0007] Therefore, as a method of reducing the sliding friction generated on the sliding surface between the roller head and the large flange portion of a tapered roller bearing, the method of reducing the tiny surface irregularities (roughness) existing on the sliding surface without increasing the viscosity of the lubricating oil and increasing the oil film thickness has become the main method for reducing sliding friction.

[0008] Here, an attempt has been made to predict a function of the oil film parameter Λ representing the contact state of sliding members with respect to the sliding friction generated on the sliding surfaces between the roller head and the large flange portion (Non-Patent Document 1). In the method described in this document, the root mean square roughness Rq is used as a parameter representing the roughness of the surface to estimate the sliding friction generated on the sliding surfaces between the roller head and the large flange portion of the tapered roller bearing.

[0009] Prior Art Documents

[0010] Non-Patent Documents

[0011] Non-Patent Document 1: S. Aihara, ″A new running torque formula for tapered roller bearings under axial load″, Transactions of the ASME. Journal of tribology, vol. 109, 1987, pp471 - 478

[0012] Non-Patent Document 2: Yuji Yamamoto, Hiroshi Kanda, Tribology, P124

[0013] Non-Patent Document 3: Tokunaga - Sugimura - Yamamoto: Development and Performance Evaluation of a Mechanical Seal with a Sealing Mechanism and a Friction Reduction Mechanism - Experimental Study -, Tribologist, 60, 5(2015)332.

[0014] Non-Patent Document 4: Kanda: Micro EHL, Tribologist, 35, 1(1990)8.

[0015] Non-Patent Document 5: I. Krupka, R. Poliscuk, M. Hartl: Behavior of thin viscous boundary films in lubricated contacts between micro - textured surfaces, Tribology Int., 42, (2009)535.

[0016] Non-Patent Document 6: Maeda - Maruyama - Nakano: Simultaneous Measurement of Film Thickness and Rupture Ratio in EHD Contact - Verification of Impedance Method, Tribology Conference 2017 Autumn Takamatsu, Proceedings, A39 Summary of the Invention

[0017] Problems to be Solved by the Invention

[0018] However, the inventors of the present application conducted in-depth research and identified the following issues: As described in detail later, if the oil film parameter Λ(Rq) or Λ(Ra) is calculated using the root mean square roughness Rq or the arithmetic mean roughness Ra as a parameter representing the roughness of the surface, then in a surface shape with a deviation in the height distribution of the roughness (for example, a flat surface with grooves or holes on a smooth surface), the sliding friction generated on the sliding surfaces of two sliding parts lubricated with a lubricant cannot be intentionally summarized as a function of the oil film parameter Λ(Rq) or Λ(Ra), and the sliding friction cannot be estimated with high precision.

[0019] Therefore, the present invention has been completed with a focus on such problems, and its subject is to provide a friction design method for sliding parts, a surface roughness management method, and a manufacturing method for sliding mechanisms that can accurately estimate the sliding friction generated between the sliding surfaces of two sliding parts after lubrication with a lubricant.

[0020] Means for solving problems

[0021] In order to solve the above-mentioned problems, a friction design method for sliding parts involved in one embodiment of the present invention is characterized in that a target value of the surface roughness of the sliding surfaces of the two sliding parts to be managed as products is set based on the correlation between the friction coefficient and the oil film parameter, the friction coefficient is obtained using a sliding surface model corresponding to the sliding surfaces of the two sliding parts after lubrication with a lubricant, and the oil film parameter is calculated using the center level difference or the sum of the center level difference and the protruding peak height as a parameter representing the surface roughness in the sliding surface model.

[0022] Here, in a friction design method for a sliding component of one embodiment of the present invention, a target oil film parameter value corresponding to the target value is obtained based on the correlation between the friction coefficient and the oil film parameter, and the synthetic roughness σ* of the sliding surface corresponding to the target value is calculated based on the obtained target oil film parameter value and the estimated or actually measured oil film thickness of the lubricant on the sliding surfaces of the two sliding components. Thus, a target value of the center level difference of the surface roughness of the sliding surface to be managed as the product is set, or a target value of the sum of the center level difference of the surface roughness of the sliding surface to be managed as the product and the height of the protruding peak is set.

[0023] In the friction design method of a sliding component according to one embodiment of the present invention, two-dimensional roughness parameters (Rk, Rpk) can be used for the center level difference and the protruding peak height.

[0024] In the friction design method of a sliding component according to one embodiment of the present invention, the center level difference and the protruding peak height can use three-dimensional roughness parameters (Sk, Spk).

[0025] In addition, in order to solve the above-mentioned problems, a surface roughness management method of a sliding part involved in one embodiment of the present invention is characterized in that, using a friction design method of one embodiment of the present invention, a target value of the center level difference of the surface roughness of the sliding surface to be managed as the product, or a target value of the sum of the center level difference of the surface roughness of the sliding surface and the height of the protruding peak is used as a qualified benchmark for the roughness when processing the surface of the sliding part.

[0026] Here, in one embodiment of the surface roughness management method of a sliding part of the present invention, as a qualified standard for the roughness during the processing, management can also be performed based on whether the value of the ratio Svr of the valley portion of the surface unevenness in the sliding surface to be managed as the product satisfies the following (formula).

[0027] Svr≤specified value······(Formula)

[0028] Here, Svr is the ratio of the valleys of the surface unevenness in the sliding surface calculated based on 100-Mr2, 100-Rmr, 100-Smr2 or 100-Smr, wherein Mr2 and Rmr are two-dimensional roughness parameters, Mr2 is the load length ratio of the center portion (English: core) of the sliding surface to be managed as the product, Rmr is the relative load length ratio of the sliding surface to be managed as the product, Smr2 and Smr are three-dimensional roughness parameters, Smr2 is the load area ratio of the center portion of the sliding surface to be managed as the product, and Smr is the relative load area ratio of the sliding surface to be managed as the product. In addition, the range specified by the above (formula) is the range in which the deviation Δμ from the reference is less than a certain value.

[0029] In addition, in order to solve the above-mentioned problems, a manufacturing method of a sliding mechanism according to one embodiment of the present invention is a method for manufacturing a sliding mechanism composed of sliding surfaces between two sliding parts and a lubricant for lubricating the sliding surfaces between the two sliding parts, characterized in that the sliding mechanism is manufactured using sliding parts that are deemed to be qualified products through the surface roughness management method of sliding parts according to one embodiment of the present invention.

[0030] Furthermore, to address the aforementioned issues, another embodiment of the present invention provides a method for managing the surface roughness of a sliding component, characterized in that friction is measured under rolling sliding conditions using grooved balls, and based on the measurement results, the groove area ratio of the grooves is managed to a value below a predetermined value in a manner that satisfies the desired surface roughness management conditions. For example, the grooves are parallel grooves. Furthermore, the grooves are not limited to parallel grooves and may also be straight grooves orthogonal to the sliding direction, cross grooves, circumferential grooves, random grooves without a specific directionality in the groove direction, grooves without continuity, or depressions.

[0031] Based on the embodiments, as described later, another aspect of the present invention of the surface roughness management method for sliding parts is based on the results of confirming the oil film thickness of the groove under rolling sliding conditions and its influence on friction, and the following insights are obtained: the oil film thickness is locally reduced at the groove edge of the groove, and in addition, depending on the difference in the groove area ratio, the oil film thickness is reduced not only at the groove edge but also as a whole. Therefore, in the mixed lubrication area, as the groove area ratio of the groove increases, the friction increases. In the fluid lubrication area, although the influence of the groove area ratio in the mixed lubrication area is not reached, if the depth of the groove becomes deeper, the friction increases slightly.

[0032] Thus, according to another aspect of the present invention, a surface roughness management method can be configured to reduce the groove area ratio to a predetermined value or less, based on this knowledge, so as to satisfy desired surface roughness management conditions. Therefore, according to the present invention, a surface roughness management method can be provided that satisfies desired surface roughness management conditions under rolling sliding conditions when grooves are present on the surface.

[0033] Effects of the Invention

[0034] According to the present invention, it is possible to estimate with high accuracy the sliding friction generated between the sliding surfaces of two sliding members lubricated with a lubricant. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a flow chart showing a friction design, management, and manufacturing method according to one embodiment of the present invention. The flow chart uses the correlation between the friction coefficient μ and the oil film parameters Λ(Rk) and Λ(Rk+Rpk) to sequentially illustrate the steps of the friction design, management, and manufacturing method for the surfaces of two sliding parts lubricated with a lubricant.

[0036] Figure 2 This is a schematic diagram illustrating an example of a friction test device and test conditions used in the friction design, management, and manufacturing method of the present embodiment.

[0037] Figure 3This figure illustrates an example of application of a sliding mechanism consisting of sliding surfaces between two sliding parts and a lubricant that lubricates the sliding surfaces between the two sliding parts to the roller head and the opposing surfaces of the large flange portion of a tapered roller bearing. (a) of the figure is a schematic diagram of the main part, and (b) of the figure is a partially enlarged view of (a).

[0038] Figure 4 It is a graph showing an example of two surfaces having substantially the same arithmetic mean roughness Ra (random surface (a), flat surface (b)).

[0039] Figure 5 This is a graph showing an example of measurement results of sliding friction on random surfaces and flat surfaces.

[0040] Figure 6 (a) to (g) are histograms showing the surface roughness distribution in the sliding surface model used in the friction test used in the friction design, management, and manufacturing method of the present embodiment.

[0041] Figure 7 It means targeting Figure 6 The graph shows the relationship between the oil film parameter Λ(Rq) calculated using the root mean square roughness Rq and the friction coefficient μ for the sliding surface model shown.

[0042] Figure 8 (a) and (b) are graphs illustrating the state of the oil film between the sliding surfaces of two sliding parts lubricated with a lubricant.

[0043] Figure 9 It is an explanatory diagram of the center level difference Rk and the protruding peak height Rpk (JIS B0671).

[0044] Figure 10 It is an explanatory diagram of the center level difference Rk and the protruding peak height Rpk (JIS B0671).

[0045] Figure 11 It is aimed at Figure 6 The sliding surface model shown is a graph showing the correlation between the oil film parameter Λ(Rk) calculated using Rk as the roughness parameter and the friction coefficient μ ((a) of the figure), and the correlation between the oil film parameter Λ(Rk+Rpk) calculated using Rk+Rpk as the roughness parameter and the friction coefficient μ ((b) of the figure).

[0046] Figure 12 This is a diagram showing an example of the profile and histogram of a surface having upward convexities and downward convexities on a sliding surface.

[0047] Figure 13(a), (b), and (c) are diagrams showing images of surfaces having the same roughness parameter Rk but different ratios of rough valleys.

[0048] Figure 14 This is a schematic diagram for explaining the calculation method of Δμ.

[0049] Figure 15 (a) shows the relationship between 100-Mr2 of the ratio Svr of the valley portion showing the surface unevenness and the depth Rvk of the protruding valley portion, Figure 15 (b) shows the relationship between 100-Rmr of the ratio Svr of the valley portions showing the surface irregularities and the depth Rvk of the protruding valley portions.

[0050] Figure 16 This is a graph showing an example of a shape in which the height distribution of roughness has deviations (a surface having deep grooves at a smaller roughness).

[0051] Figure 17 This is a diagram illustrating an example of the three-dimensional shape of the surface of a test piece used in a test according to one embodiment of the present invention.

[0052] Figure 18 1 and 2 are diagrams showing examples of interference images and cross-sectional shapes of central oil films measured by optical interferometry.

[0053] Figure 19 This is a graph showing the friction coefficient and oil film thickness at various speeds.

[0054] Figure 20 This is a graph showing the relationship between the actual measured oil film thickness and the friction coefficient.

[0055] Figure 21 (a) represents the roughness curve and its load curve, Figure 21 (b) shows the load curves of roughness for different cut-off levels. DETAILED DESCRIPTION

[0056] An embodiment of the present invention (including examples) will be described below with appropriate reference to the accompanying drawings. The accompanying drawings are schematic. Therefore, it should be noted that the relationship and ratio between thickness and planar dimensions may differ from those in reality, and that the drawings may also contain portions with different dimensional relationships and ratios.

[0057] The embodiments (including examples) described below illustrate devices and methods for embodying the technical concept of the present invention, and the technical concept of the present invention does not specify the materials, shapes, structures, arrangements, etc. of the constituent components to the following embodiments.

[0058] For example, in order to obtain the correlation between the friction coefficient and the oil film parameters, it is not necessary to Figure 2 Such friction test equipment, on the other hand, rotates the tapered roller bearing itself and obtains the torque generated at this time.

[0059] [Friction Design Method of the Present Embodiment, Roughness Management Method Using the Friction Design Method, and Sliding Mechanism Manufacturing Method]

[0060] The following method is described: using a sliding surface model corresponding to the sliding surfaces of two sliding parts lubricated with a lubricant, the surface roughness of the two sliding parts as products is designed, managed, and manufactured based on the relationship between μ and Λ obtained by experimentally measuring the relationship between the friction coefficient μ and the oil film parameter Λ.

[0061] In particular, in the friction design method, surface roughness management method, and sliding mechanism manufacturing method of the present embodiment, the oil film parameter Λ(Rk) or Λ(Rk+Rpk) is calculated using the center level difference Rk or Rk+Rpk as a parameter representing the roughness of the sliding surfaces of the lubricated sliding components. The sliding friction generated between the lubricated sliding surfaces of the sliding components is controlled to achieve a target friction coefficient μ. The surface roughness of the sliding surfaces of the two target sliding components is designed and managed, and a sliding mechanism is manufactured using the two sliding components. In this specification, a sliding mechanism refers to a mechanical structure comprising the sliding surfaces of two sliding components and a lubricant that lubricates the sliding surfaces of the two components. For example, the facing surfaces of the roller head and large flange of a tapered roller bearing can be used as this sliding mechanism.

[0062] In detail, Figure 1 As shown in the process flow of the processing steps in step S1, the operating conditions (rolling speed, load, temperature, lubricant viscosity, etc.) to be managed as a product and the target friction coefficient μ are set [Process 1]. In the example of this embodiment, when using Figure 2 In the friction testing apparatus 10 shown, the target friction coefficient μ is set to μ≦0.05 under predetermined operating conditions A in a friction test based on a sliding surface model.

[0063] like Figure 2 As shown in FIG. 1 , the test apparatus 10 constitutes a sliding surface model corresponding to the sliding surfaces of two sliding parts lubricated with a lubricant. Specifically, the test apparatus 10 comprises a drive shaft 1 with its axis arranged vertically, and a steel disk (diameter 100 mm) corresponding to one sliding part is supported horizontally at the upper end of the drive shaft 1. ) 2. On the lower surface of the steel disk 2, a steel ball (diameter 1.5 mm) corresponding to the other sliding member is pressed with a predetermined surface pressure L. ) 3. The steel balls 3 are supported by a horizontal rotating shaft 4 so as to be rotatable around the rotating shaft 4.

[0064] In addition, in this embodiment, the "prescribed operating conditions A" in the test device 10 are: test oil: Durasyn 166 (31 cSt @ 40°C), test temperature: 25°C (room temperature), slip rate: 15%, rolling speed: 0.1 m / s, load: 9.8 N, and surface pressure: 0.5 GPa.

[0065] Then, if Figure 1 As shown, in the next step S2, for a sliding surface model corresponding to the sliding surfaces between the two sliding members 2 and 3 lubricated with lubricant, the relationship between the friction coefficient μ and the oil film parameter Λ is measured by an experiment using a friction testing device 10 [process 2].

[0066] In this embodiment, in order to measure the relationship between the oil film parameter Λ and the friction coefficient μ over a wide range (0 < Λ < 3 or more), Figure 2 In the friction test of the friction test apparatus 10 shown in FIG, under the predetermined operating condition B, a plurality of surfaces 1 to 6 with different surface roughness were used as sliding surface models corresponding to the sliding surfaces between two sliding members 2 and 3 lubricated with a lubricant. The surface roughness used as the sliding surface model is shown in Tables 1 and Figure 6 .

[0067] The specified operating condition B refers to:

[0068] Test oil: Durasyn 166 (31 cSt @ 40°C), test temperature: 25°C (room temperature), slip rate: 15%, rolling speed: 0.01 m / s to 0.5 m / s, load: 9.8 N, surface pressure: 0.5 GPa.

[0069] [Table 1]

[0070]

[0071] In addition, for Table 1 and Figure 6 The results of measuring the friction coefficients of the surfaces 1 to 6 of the plurality of sliding surface models shown in FIG. 1 and FIG. 2 are shown in FIG. 3 and 4. Figure 11 .in addition, Figure 11 The oil film thickness h under each condition was calculated according to the Hamrock-Dowson oil film formula, and the oil film parameter Λ at each test point was calculated based on the surface roughness shown in Table 1 and used for the horizontal axis of the graph.

[0072] Here, in this embodiment, the surface roughness σ is not represented by the root mean square roughness Rq, but the surface roughness σ is represented by the level difference Rk of the center, or the sum of the level difference Rk of the center and the height Rpk of the protruding peak, Rk+Rpk, to calculate the composite roughness σ*. In addition, in this embodiment, the square root of the sum of the squares of the roughness values ​​(σ1 2 +σ2 2 ) 0.5 To calculate the synthetic roughness σ* required when summarizing the correlation using the oil film parameter Λ.

[0073] However, if the relationship between the oil film parameter Λ(Rk+Rpk) and the friction coefficient μ can be well summarized by expressing the composite roughness σ* as the sum of the roughnesses (σ1+σ2), then the square root of the sum of squares (σ1) can also be used. 2 +σ2 2 ) 0.5 , and (σ1+σ2) is used to represent the composite roughness σ*. Here, Rk+Rpk is used as the surface roughness, and the square root of the sum of the squares of each roughness (σ1 2 +σ2 2 ) 0.5 Example of calculating the composite roughness σ*.

[0074] Then, in Figure 1 In step S3, based on the relationship between the oil film parameter Λ(Rk+Rpk) and the friction coefficient μ obtained in step S2, the value of the target oil film parameter Λ(Rk+Rpk) that meets the target and should be managed as a product is calculated [process 3].

[0075] Specifically, using data near the target value μ = 0.05, an approximate curve representing the correlation between the friction coefficient μ and the oil film parameter Λ(Rk + Rpk) was calculated. The value of the oil film parameter Λ(Rk + Rpk) represented by this approximate curve when μ = 0.05 was used as the target oil film parameter Λ(Rk + Rpk). As a result, the target oil film parameter Λ(Rk + Rpk) value was Λ(Rk + Rpk) = 0.49.

[0076] In the following step S4, the oil film thickness h formed between the sliding surfaces of the two sliding members 2 and 3 under the predetermined operating conditions A of the friction testing apparatus 10 in step S1 is calculated using the Hamrock-Dowson oil film formula for point contact EHL in Non-Patent Document 2 (Step 4). The result shows that the oil film thickness h is 0.063 μm. The oil film formula used in this embodiment to calculate the oil film thickness h will be described later.

[0077] Next, in step S5, the target composite roughness σ* is calculated based on the oil film parameter Λ(Rk + Rpk) and the oil film thickness h obtained in steps 3 and 4 (step 5). In the example of this embodiment, σ(Rk + Rpk)* is 0.129 μm based on Λ(Rk + Rpk) = 0.49 and h = 0.063 μm.

[0078] Next, in step S6, the surface roughness satisfying σ*〔=(σ12+σ22)0.5〕 obtained in step 5 is used as the target value to be managed as a product [step 6]. When the roughness of the solid surfaces of the two sliding parts 2 and 3 is the same, the surface roughness is σ* divided by In the example of this embodiment, σ(Rk+Rpk)*=0.129 μm, and therefore, when the two sliding members 2 and 3 have the same surface roughness, Rk+Rpk=0.091 μm.

[0079] Next, in step S7, in order to obtain the desired product, after the sliding surfaces of the two sliding parts 2 and 3 are processed, the surface roughness of the processed sliding surfaces is measured, and the level difference Rk of the center part, the height of the protruding peak Rpk, and the load length ratio Mr2 of the center part are calculated [process 7].

[0080] The measurement in step 7 basically complies with JIS B0633, but the measurement position is not necessarily any position on the sliding surface, but the position where the two sliding members 2 and 3 are in contact with each other is measured.

[0081] Here, Figure 3 A tapered roller bearing is shown. As shown in this figure, a tapered roller bearing 20 has multiple tapered rollers 13 roamingly sandwiched between an outer ring 11 and an inner ring 12. A large flange 14 is formed on one side of the inner ring 12, with which the roller heads 13t of the tapered rollers 13 contact. A relief groove 15 is formed at the boundary between the large flange 14 and the raceway surface. Reference symbol R in this figure represents the roller head radius, and reference symbol H represents the height of the contact point between the facing surface 14t of the large flange and the roller head 13t.

[0082] The axial load acting on the tapered roller bearing 20 is primarily supported by the facing surface 14t of the large flange 14 and the roller head 13t of the tapered roller 13. Furthermore, the contact area between the facing surface 14t of the large flange 14 and the roller head 13t forms a contact ellipse d calculated based on Hertzian contact theory. This contact ellipse d varies depending on the geometry of the facing surface 14t of the large flange 14 and the roller head 13t, as well as the flange load acting on the large flange 14.

[0083] Therefore, for example, when the product is the tapered roller bearing 20 and the present invention is applied to the facing surface 14t of the roller head 13t and the large flange portion 14 of the tapered roller bearing 20, the roughness at the position of the contact point height H between the roller head 13t and the facing surface 14t of the large flange 14 is measured as the portion corresponding to the two sliding parts 2 and 3.

[0084] The evaluation length is preferably controlled within the contact ellipse d. Regarding the measurement direction, if the roughness has a directionality, measurement is performed perpendicular to the scratch. If there are multiple directions of directionality or no specific directionality is determined, the roughness is measured in the direction that yields the maximum value. Parameter calculation complies with JIS B0671-2 (ISO 13565-2 in ISO).

[0085] Then, in Figure 1 In step S8, if the surface roughness of the sliding surface processed to become the desired product and the ratio of the valleys of the surface unevenness are below the specified value, it becomes a qualified product with a friction coefficient below the target [process 8→completed]. The roughness is the roughness that meets the target value that should be managed as a product obtained in the above-mentioned process 6.

[0086] On the other hand, if the surface roughness of the sliding surface processed to become the desired product, or the ratio of the valleys of the surface unevenness, does not meet the specified value, the surface of the sliding surface is reprocessed [Process 8 → Reprocessing], and the process returns to step S7. The roughness is the roughness that meets the target value that should be managed as a product obtained in the above-mentioned process 6.

[0087] Therefore, according to the sliding component friction design method, surface roughness management method, and sliding mechanism manufacturing method of the present embodiment, it is possible to estimate with high accuracy the sliding friction generated between the sliding surfaces of two sliding components lubricated with a lubricant.

[0088] Therefore, for example, the friction between the roller head and the large flange of a tapered roller bearing can be designed with high precision based on the opposing surfaces between the roller head and the large flange, and can be managed to a surface roughness Rk or less than the roughness of Rk+Rpk determined thereby.

[0089] Furthermore, using sliding components that have been certified as qualified using this surface roughness management method, it is possible to manufacture the sliding mechanism of, for example, a tapered roller bearing (the portion between the facing surfaces of the roller head and the large flange). This can improve process capabilities and production efficiency for roughness management of the roller head and large flange of tapered roller bearings.

[0090] [About the oil film parameter Λ]

[0091] Next, the friction design method and management method of the sliding component and the manufacturing method of the sliding mechanism according to the above-mentioned embodiment will be described in more detail with reference to verification examples and the like.

[0092] First, the oil film parameter Λ will be described in detail. Here, the film thickness ratio (oil film parameter) Λ calculated according to the following (Equation 1) has been used as a parameter representing the degree of interference between rough protrusions in the contact portion of the sliding surfaces of two sliding parts under lubrication.

[0093] Λ=h / σ*……(Formula 1)

[0094] Here, h is the thickness of the lubricant film on the sliding surfaces of the two sliding parts, and σ* is the combined roughness of the sliding surfaces of the sliding parts. σ* is given by the following (Equation 2).

[0095]

[0096] Conventionally, σ1 and σ2 are represented by the root mean square roughness Rq and the arithmetic mean roughness Ra (JIS B0601), which represent the standard deviation of the roughness of the sliding surfaces of sliding parts. In the following formula, l is the reference length, and Z(x) is the height at any position x on the surface.

[0097] [Mathematical formula 1]

[0098]

[0099] [Issues in Conventional Friction Design and Management Methods]

[0100] Here, the oil film parameter Λ represents the degree of interference between projections of sliding parts, and is therefore known to have a significant correlation with friction.

[0101] However, the present inventors' research has revealed that, through verification, if the oil film parameters Λ(Rq) or Λ(Ra) are calculated using the root mean square roughness Rq or the arithmetic mean roughness Ra as parameters representing the surface roughness, then in shapes with deviations in the roughness height distribution (flat surfaces with grooves or holes on a smooth surface), there may be cases where the sliding friction generated between the sliding surfaces of two sliding parts under lubrication cannot necessarily be intentionally summarized.

[0102] Figure 4 Examples (a) and (b) show two surfaces with approximately the same arithmetic mean roughness Ra. Figure 4 The two surfaces shown have approximately the same arithmetic mean roughness Ra, using Figure 2 The test apparatus 10 shown was subjected to a friction test under the operating conditions specified in the above-mentioned specification A.

[0103] For the two surface examples (a) and (b), the results of the friction test using the test device 10 are as follows: Figure 5 As shown, it can be seen that the sliding friction of a flat surface ((b) in the figure) is smaller than that of a random surface ((a) in the figure). This indicates that the sliding friction cannot be predicted or managed using the arithmetic mean roughness Ra.

[0104] To verify this, a friction test was conducted using the test apparatus 10 under the operating conditions specified in the above-mentioned B for the sliding surface model shown in Table 1. The relationship between the oil film parameter Λ and the friction coefficient μ was obtained, and the correlation between the oil film parameter Λ and the friction coefficient μ was verified. In this friction test, the surface roughness distribution used as the sliding surface model is Figure 6 The graphs (a) to (g) are shown.

[0105] In addition, in order to understand the distribution of concave and convex surfaces of each sliding surface model, the histogram of each sliding surface model surface is also shown. Figure 6 The right side of each figure (a) to (g). From the histogram of each sliding surface model surface shown in the figure, it can be seen that surfaces 1 to 3 are random surfaces with surface unevenness distribution close to normal distribution, and surfaces 4 to 6 are planes with surface unevenness distribution deviation.

[0106] The surface roughness parameters of each sliding surface model are shown in Table 1. Since surface roughness varies somewhat depending on the measurement location, Table 1 shows the average values ​​measured at multiple locations on each sliding surface model surface.

[0107] In order to obtain the relationship between the oil film parameter Λ and the friction coefficient μ, the oil film thickness h at each experimental point was calculated based on the Hamrock-Dowson oil film formula (※Non-patent document 2), and the oil film parameter Λ at each experimental point was calculated based on the surface roughness shown in Table 1. In addition, the synthetic roughness σ* required for the induction of the oil film parameter Λ was obtained by the square root of the sum of the squares of the roughness values ​​(σ1 2 +σ2 2 ) 0.5 Calculate the surface roughness σ using the root mean square roughness Rq.

[0108] The oil film formula in the Hamrock-Dowson point contact EHL in Non-Patent Document 2 is as follows.

[0109] H=h / Rx……(Formula 3)

[0110] Here, h is the oil film thickness, H is the line thickness, and Rx is the equivalent radius of the surface containing the x-axis (direction of motion). The oil film thickness h can be either the center film thickness or the minimum film thickness, but the center film thickness is used for calculation in Table 1. Calculate the line thickness H below and substitute it into (Equation 3) to determine the oil film thickness.

[0111] Central film thickness: Hc = 2.69U 0.67 ·G 0.53 W -0.067 {1-0.61exp(-0.73k)}

[0112] Minimum film thickness: Hmin = 3.63U 0.68 ·G 0.49 W -0.073 {1-exp(-0.68k)}

[0113] Here, W, G, U, and k are dimensionless display quantities given by the following equations.

[0114] W=w / (ERx 2 )

[0115] G=αE

[0116] U=(η0 u ) / (ERx)

[0117] k=a / b=1.03(Ry / Rx) 0.64

[0118] Wherein, u is the rolling speed, η0 is the viscosity at atmospheric pressure, α is the pressure viscosity coefficient, w is the load, E is the equivalent elastic coefficient, a and b are the contact ellipse radius in the direction x and the direction y at right angles to the direction x.

[0119] In addition, in the verification example of this embodiment, the oil film thickness is calculated by the Hamrock-Dowson oil film formula for calculating the oil film thickness of the point contact EHL, but it is not limited to this. In addition, the oil film thickness can also be calculated using the Blok-Mores formula, the Greenwood-Johnson formula, the Dowson-Higginson formula for calculating the oil film thickness of the line contact EHL, etc., and the values ​​actually measured by the optical interference method, the electrostatic capacitance method, the contact resistance method (for example, refer to non-patent document 6), the impedance method, etc. can also be used.

[0120] exist Figure 7 Graphs showing the relationship between the oil film parameter Λ(Rq) calculated using the root mean square roughness Rq obtained by the above method and the friction coefficient μ are shown in FIG.

[0121] As described above, it is known that the sliding friction generated between the sliding surfaces of the two sliding members 2 and 3 lubricated with a lubricant is correlated with the Λ value (oil film parameter or film thickness ratio), which is a value obtained by dividing the thickness of the oil film formed between the two surfaces by the composite roughness calculated from the root mean square roughness Rq (or arithmetic mean roughness Ra) of the sliding member (see Figure 7 Surfaces 1 to 3 indicated by symbols ○, △, and ×).

[0122] However, the inventors of the present application have conducted verification and found that the height distribution of the roughness of the sliding surfaces of two sliding parts lubricated with lubricant is not a normal distribution, and there is a deviation on the flat surface (see Figure 7 In the case of surfaces 4 to 6) indicated by the symbols □, ◇, and *, as Figure 7 As shown, the curves are different from those of surfaces 1 to 3 having a random uneven distribution. Under the oil film parameter Λ(Rq) calculated based on the root mean square roughness Rq, the sliding friction generated between the sliding surfaces of the sliding parts lubricated with the lubricant cannot be summarized as a whole.

[0123] Specifically, as shown in the figure, surfaces 1 through 3 in the sliding surface model are random surfaces (surfaces with a roughness height distribution close to a normal distribution), while surfaces 4 through 6 in the sliding surface model are flat surfaces (surfaces with no rough protrusions and a skewed distribution of asperities). As can be seen from the above, the oil film parameter Λ(Rq), calculated from the root mean square roughness Rq, cannot be used to manage the sliding friction between surfaces with widely varying asperity height distributions.

[0124] This is because, as can be seen from the formula shown above, parameters such as the root mean square roughness Rq are calculated based on the overall surface profile. If there are a large number of deep valleys and troughs on the surface, the value of Rq will be affected by them and become larger, and the oil film parameter Λ(Rq) calculated based on this value will be calculated to be smaller.

[0125] Therefore, compared to random faces (faces with height distribution close to normal distribution), the plane is drawn on Figure 7 That is, under the same root mean square roughness Rq, the sliding friction generated on the sliding surfaces of sliding parts lubricated with lubricant is smaller on a flat surface than on a random surface.

[0126] Now, if Figure 8 As shown, it is assumed that the oil film between the sliding surfaces of the sliding parts 2 and 3 after lubrication with lubricant is formed not by the average value of the entire surface profile ((a) in the figure), but by the average line of the part with a high probability of existence on the surface ((b) in the figure).

[0127] Here, as a parameter indicating the roughness of the "high probability portion of the surface", there is a level difference Rk at the center (JIS B0671). In the present invention, this roughness parameter Rk and Rpk indicating the height of the rough protrusions are used as parameters indicating the surface roughness. The roughness parameters Rk and Rpk refer to Figure 9 as well as Figure 10 The graph shown is calculated using the following (※) steps.

[0128] (※)

[0129] The equivalent straight line is obtained at the center of the load curve (S-shaped load curve with a single inflection point) including 40% of the measurement points of the roughness curve. Figure 9 As shown, the "center portion" is located at a position where the slope of the secant of the load curve obtained by setting the difference ΔMr of the load length ratio to 40% is the gentlest.

[0130] This is calculated by moving the secant line at ΔMr = 40% from Mr = 0% along the load curve as shown in the figure. The secant line at ΔMr = 40%, which has the gentlest slope, becomes the center of the load curve used to calculate the equivalent straight line. If there are multiple sections with the gentlest slopes, the first area found becomes the "center." For the "center," calculate the straight line (equivalent straight line) that minimizes the sum of the squares of the deviations in the vertical axis direction.

[0131] In addition, Figure 10 The areas enclosed by the load curves above and below the center, represented by Rk, are shaded. They are equal to the cross-sectional areas of the protruding peaks and protruding valleys outside the center of the roughness curve. The parameter Rpk is given by the height of a right triangle equal to the cross-sectional area of ​​the protruding peaks, and the parameter Rvk is given by the height of a right triangle equal to the cross-sectional area of ​​the protruding valleys (see Figure 10 The base of the right triangle corresponding to the cross-sectional area A1 of the protruding peak is Mr1, and the base of the right triangle corresponding to the cross-sectional area A2 of the protruding valley is Mr2. The difference between Mr1 and Mr2 is 100%.

[0132] (※Finish)

[0133] exist Figure 11 In the figure, as a roughness parameter, the level difference Rk of the center part, or the relationship between the oil film parameter Λ(Rk) calculated using the level difference Rk of the center part and the friction coefficient μ ((a) of the figure), and the relationship between the oil film parameter Λ(Rk+Rpk) calculated using Rk+Rpk which is the sum of the height Rpk of the protruding peak part and the friction coefficient μ ((b) of the figure) are shown.

[0134] As shown in the verification example in the figure, if the oil film parameter Λ(Rk) or Λ(Rk+Rpk) calculated using Rk or Rk+Rpk is used as the roughness parameter, then Figure 6 All of the surfaces 1 to 6 in the sliding surface model shown can meaningfully summarize the sliding friction (friction coefficient μ) generated on the sliding surfaces between the sliding parts lubricated with the lubricant.

[0135] Thus, the inventors of the present application conducted intensive research and obtained the following findings: as a parameter expressing the roughness of the sliding surfaces of sliding parts lubricated with a lubricant, Figure 11 As shown, if the oil film parameter Λ(Rk) or Λ(Rk+Rpk) is obtained by dividing by the composite roughness σ* calculated using the level difference Rk of the center ((a) of the figure) or Rk+Rpk (the sum of the level difference of the center and the height of the protruding peak ((b) of the figure)), the sliding friction generated between the sliding surfaces of two sliding parts lubricated with a lubricant can be deliberately summarized regardless of the surface.

[0136] This result indirectly shows that, in the case of a surface with uneven distribution such as a plane shape, the oil film is not Figure 8 The rough overall average line shown in (a) is used as the basis, but Figure 8 The above assumption based on the average line of the portion with a high proportion of surface irregularities (the center portion of the roughness) as shown in (b) is correct.

[0137] That is, for example, if the parameters representing the surface roughness of the roller head and large flange of a tapered roller bearing are summarized using the oil film parameters Λ(Rk) and Λ(Rk+Rpk) calculated using the level differences Rk and Rk+Rpk at the center, then regardless of whether there are deviations in the distribution of convex and concave shapes in the surface shape, they can be plotted on a single main curve, thereby enabling high-precision estimation of sliding friction.

[0138] Regarding which of Rk and Rk+Rpk is used to calculate the oil film parameter Λ (i.e. Λ(Rk) or Λ(Rk+Rpk)), for Figure 6 For planes that are significantly convex downward and have stepped portions, such as surfaces 4 to 6 shown, the membrane parameter Λ can be calculated using either Rk or Rk+Rpk.

[0139] However, the inventors have confirmed through verification that: Figure 12 In the case of a surface having upward and downward projections as in the example shown in , the sliding friction can be more neatly summarized by using Rk+Rpk to calculate the oil film parameter Λ(Rk+Rpk).

[0140] In addition, the inventors have confirmed that the roughness of the solid surface can be intentionally summarized even if it is not based on linear roughness such as Rk and Rpk, but using the oil film parameter Λ (i.e., Λ(Sk) or Λ(Sk+Spk)) calculated based on the level difference Sk of the center part and the height of the protruding peak Spk of the surface roughness (three-dimensional surface properties: JIS B0681-2, "ISO 25178-2" in ISO), and Sk and Sk+Spk can also be used as parameters representing the roughness of the solid surface.

[0141] In addition, the inventors have also confirmed through verification that the oil film parameters Λ (i.e., Λ(Sa), Λ(Sq)) calculated based on the arithmetic mean roughness Sa and root mean square roughness Sq of the surface roughness still cannot accurately summarize the sliding friction generated on the sliding surfaces of sliding parts after lubrication with lubricant.

[0142] Here, the friction coefficient μ can be summarized based on the oil film parameters Λ(Rk) and Λ(Rk+Rpk) calculated from the roughness parameters Rk and Rpk, which means that the rough valleys do not significantly affect the friction.

[0143] However, although it does not have a significant impact on friction, it does not mean that the presence of any number of rough valleys is acceptable. For example, Figure 13 (a), (b), and (c) are images showing surfaces with different ratios of rough valleys under the same roughness parameter Rk.

[0144] Therefore, the following experiment was conducted to verify the degree of valley roughness that can be used to effectively summarize the friction coefficient μ using the oil film parameter Λ(Rk) or Λ(Rk+Rpk) calculated using the roughness parameters Rk and Rpk. In this experiment, a sliding surface model with varying ratios and depths of valley roughness was prepared. Figure 2 The friction test device 10 shown was tested under the following predetermined operating conditions C.

[0145] The specified operating conditions C are: test oil: Durasyn 162 (5.5 cSt @ 40°C), Durasyn 166 (31 cSt @ 40°C), Durasyn 170 (65 cSt @ 40°C), test temperature: 25°C (room temperature), slip ratio: 15%, rolling speed: 0.01 m / s to 0.5 m / s, load: 9.8 N, and surface pressure: 0.5 GPa.

[0146] Table 2 shows the roughness of test pieces 1 to 24 used in the verification test as sliding surface models. Surfaces 1 to 18 are disc test pieces, and friction tests were conducted with ball A shown in Table 3. Surfaces 19 to 24 are ball test pieces, and friction tests were conducted with disk B shown in Table 3.

[0147] In addition, the table also shows a value Δμ, which is the relationship between the oil film parameter Λ and the friction coefficient μ obtained through experiments. When the oil film parameter is a specified value, the sliding friction deviation obtained on each surface is calculated based on a surface with random roughness.

[0148] Here, as the oil film parameter, Λ(Rk+Rpk) calculated from Rk+Rpk is used, and Δμ is calculated when its value is 0.3. Alternatively, Λ(Rk) can be used as the oil film parameter, and the prescribed value can be a value other than 0.3 and can be determined arbitrarily. In addition, for the surface with random roughness used as a reference, surface 1 is used among surfaces 1 to 18, and surface 19 is used among surfaces 19 to 24. The schematic diagram for calculating Δμ is as follows Figure 14 shown.

[0149] [Table 2]

[0150]

[0151] [Table 3]

[0152]

[0153] Figure 15 (a) shows a graph of 100-Mr2, which represents the valley depth of surface unevenness, using the protruding valley depth Rvk on the X-axis and the center load length ratio Mr2 on the Y-axis. Furthermore, in this graph, with surface 1 or surface 19 having random roughness as a reference, deviations Δμ from the reference of less than 0.03 are indicated by a circle, and those greater than 0.03 are indicated by an x.

[0154] As shown in the figure, the maximum value of 100-Mr2, which satisfies Δμ < 0.03, is found on surface 17 at 33.9% of surfaces 1 to 24. Therefore, when 100-Mr2 exceeds 33.9% (the dashed line in the figure), the deviation Δμ from the reference exceeds 0.03. In other words, when 100-Mr2 > 33.9%, even if the oil film parameter Λ(Rk + Rpk) is calculated using Rk + Rpk, the friction coefficient μ is likely to be inaccurately calculated.

[0155] The primary reason is believed to be that the oil film formed based on the average line of the center section is affected by the increase in the proportion of rough valleys, causing the reference line to shift toward the valleys. Another possible cause is that the increased proportion of rough valleys increases the slope of the sliding line used in Rk calculations, leading to a larger calculated Rk.

[0156] That is, based on the correlation between the friction coefficient in the sliding surface model corresponding to the sliding surfaces of the two sliding parts 2 and 3 lubricated with the lubricant, and the oil film parameter Λ(Rk) or Λ(Rk+Rpk) calculated using the center level difference Rk or the sum of the center level difference Rk and the protruding peak height Rpk as a parameter representing the surface roughness in the sliding surface model, when setting the target value of the surface roughness of the sliding surface to be managed as a product, when intentionally summarizing the oil film parameter Λ(Rk) or Λ(Rk+Rpk) using Rk and Rpk, a more preferred surface is a surface that satisfies 100-Mr2≤33.9%.

[0157] In addition, as a method of expressing the ratio Svr of valleys in surface irregularities, the load length ratio Rmr(c) or the relative load length ratio Rmr (JIS B0601, ISO 4287) of the roughness curve may be used instead of Mr2.

[0158] The relative load length ratio Rmr is the load length ratio determined by the reference cutting level c0 and the cutting level difference Rδc of the roughness curve (refer to Figure 21 ).

[0159] Relative load length ratio Rmr = load length ratio Rmr (c1) of the roughness curve

[0160] Here, c1=c0-Rδc, c0=c(Rmr0)

[0161] Here, an example is shown in which Mr2 is substituted into Rmr0 and 0.39×Rk is substituted into Rδc to determine Rmr.

[0162] When the ratio of valleys to surface unevenness is expressed as 100-Mr2, it is found that even with random roughness, there are about 10% valleys. Therefore, a surface with large valleys in a small random roughness ( Figure 16 or Figure 17 In the case of such a surface), 100-Mr2 shows a large value compared to the ratio of the valleys visually recognized. Figure 16 In the figure, the portion surrounded by the dotted line is a smaller roughness, and the portion indicated by the arrow is a larger valley.

[0163] For example, in Figure 17In the case of 100-Mr2, the ratio is 16.2% (surface 20 in Table 2), but the actual valley ratio is 9.4% (area ratio of A in Table 4). This is because 100-Mr2 includes the valley ratio of small random roughness forming the planar part in the calculation.

[0164] On the other hand, when Rmr is obtained by substituting Mr2 into Rmr0 and substituting 0.39×Rk into Rδc, a value close to the actual valley ratio can be obtained without being affected by the small random roughness forming the planar portion.

[0165] Here, 0.39×Rk is a value corresponding to Rvk when the surface irregularities are completely random. By substituting 0.39×Rk into Rδc, the influence of the small random valleys forming the planar portion can be eliminated and only the area ratio of the large valleys can be calculated.

[0166] For example, in Figure 17 In the case of the surface, 100-Rmr is 9.8% (surface 20 in Table 2), which is close to the actual valley ratio. In the case of the valley of the surface unevenness represented by this method, the maximum value of 100-Rmr that satisfies Δμ<0.03 is 26.9% (surface 17). Figure 15 (b)), therefore, if 100-Rmr>26.9%, even if the oil film parameter Λ(Rk+Rpk) is obtained using Rk+Rpk, there is a high possibility that the friction coefficient μ cannot be summarized with high accuracy.

[0167] Here, Figure 15 (b) shows the relationship between the ratio Svr of the valleys showing the surface irregularities (100-Rmr) ​​and the depth Rvk of the protruding valleys. In this figure, with the surface 1 having random roughness as the reference, the deviation Δμ from the reference of less than 0.03 is marked with a circle, and the deviation Δμ from the reference of 0.03 or more is marked with an x.

[0168] Alternatively, 0.88×Rk (equivalent to the actual protruding valley depth Rvk* when the surface irregularities are completely random, see Figure 10 ) is substituted as the value of Rδc. In this case, the proportion of valleys of small random roughness forming the planar portion can be completely eliminated.

[0169] Thus, when using the friction design method, surface roughness management method and sliding mechanism manufacturing method of the sliding parts of the present embodiment described above, it is preferred to determine whether the surface satisfies such conditions (100-Mr2≤33.9% or 100-Rmr≤26.9%) as needed.

[0170] In addition, when calculating the ratio Svr of the valley part of the surface unevenness, it is also possible to use the three-dimensional roughness parameters (JIS B0681-2, "ISO 25178-2" in ISO) instead of Mr2, Rmr, and Rk, namely the load area ratio Smr2 of the center part, the relative load area ratio Smr, and the level difference Sk of the center part.

[0171] The relative load area ratio Smr is a parameter not defined in JIS or ISO, but can be determined from the following formula using the same procedure as for Rmr.

[0172] Relative load area ratio Smr = surface load area ratio Smr(c1)

[0173] Here, c1=c0-Rδc, c0=c(Smr0), and is calculated by setting Smr0=Smr2, and Rδc=0.39×Sk or 0.88×Sk.

[0174] In the above-described embodiment, in the friction design method for the roller head and large flange portion of a tapered roller bearing and the roughness management method using the friction design method, whether the surface satisfies the conditions based on the above-described findings is also determined.

[0175] Furthermore, in the manufacturing method of the above-mentioned embodiment, the sliding surfaces between the sliding parts 2 and 3 to be managed as products are determined, and the facing surfaces of the roller head and the large flange portion of the tapered roller bearing are used as the object, and the tapered roller bearing is manufactured using the roller head and the large flange portion whose surface roughness of the facing surfaces of the roller head and the large flange portion is managed to be a determined surface roughness Rk or a roughness below Rk+Rpk.

[0176] Furthermore, when manufacturing a tapered roller bearing, it is preferable to use Rk+Rpk as a parameter for managing the surface roughness of the sliding surface of the roller head, and to use Rk as a parameter for managing the surface roughness of the sliding surface of the large flange portion.

[0177] The reason for this is that, of the roller head and the large flange, the roller head has a higher hardness and the large flange is relatively soft, so the large flange wears early due to rotational drive and the protruding peak disappears quickly.

[0178] Therefore, as a design and management parameter, if Rk, which is easier to manage, is applied to the sliding surface of the large flange part, and Rk+Rpk, which is more difficult to manage, is applied to the sliding surface of the roller head, more efficient friction design, management and manufacturing can be achieved.

[0179] As described above, the friction design method, surface roughness management method, and sliding mechanism manufacturing method according to one embodiment of the present invention can accurately estimate the sliding friction generated between the sliding surfaces of sliding components lubricated with a lubricant. Therefore, the method can be used for friction design, surface roughness management, and manufacturing of sliding mechanisms for sliding components, such as components of rolling bearings, sliding bearings, or ball screws.

[0180] On the other hand, as previously mentioned, in the case of a surface with unevenness, such as a planar surface, it is generally not possible to summarize friction using Rq and Ra, which represent the degree of surface roughness. In other words, in the case of such a surface, it is impossible to estimate the bearing torque with high accuracy.

[0181] In contrast, the friction design method, surface roughness management method, and manufacturing method of the present invention use Rk and Rk + Rpk as roughness parameters. Therefore, the sliding friction generated between sliding surfaces of sliding components can be neatly summarized as a function of oil film parameters. Specifically, by using the methods of the present invention, for example, it is possible to accurately estimate the sliding friction generated between the roller head and large flange of a tapered roller bearing.

[0182] Furthermore, the friction design method, surface roughness management method, and manufacturing method according to one technical solution of the present invention can improve the productivity of tapered roller bearings without compromising bearing performance. Specifically, to reduce friction in systems with boundary or mixed lubrication, friction can be reduced by reducing the roughness of solid surfaces, creating a fluid lubrication state where solids do not contact each other. Therefore, surface roughness reduction requires grinding, lapping, or other processes.

[0183] However, when machining to reduce surface roughness, while rough protrusions can be removed, it is difficult to completely remove rough valleys. In such cases, the roughness parameters Rq and Ra, which are conventionally used to represent surface roughness, are the arithmetic mean and root mean square of the overall roughness, and therefore are affected by the valleys and have larger values.

[0184] For example, when the target friction roughness specification is Rq≤0.05μm, Figure 16In the case of a surface with the profile shown, Rq = 0.084 μm, thus failing the standard and being a defective surface. However, this surface has Rk = 0.071 μm and Rk + Rpk = 0.094 μm, resulting in an Rk and Rk + Rpk between those of Surfaces 1 and 2 in Table 1. Therefore, it is a surface with a random distribution of irregularities, and is assumed to be equivalent to a surface with a roughness of Rq of 0.02 μm to 0.05 μm. This surface is considered to exhibit friction less than the target friction and should be considered a qualified surface.

[0185] That is, by managing the roughness of solid surfaces using Rk and Rk+Rpk, it is possible to sort out components that are not inherently defective, and this can lead to improvements in process and production capabilities. Furthermore, conventional management methods using Rq and Ra require smoothing the entire surface, potentially reducing productivity and increasing costs.

[0186] In contrast, when managing based on Rk and Rk+Rpk, only the roughness of the portion related to friction, that is, the portion that actually supports the load, needs to be machined. Therefore, it is possible to expect a reduction in machining allowance, which leads to a reduction in cycle time (increased productivity), and a cost reduction effect due to an extension of the grinding wheel life.

[0187] The following describes tests, results, and investigations of one embodiment of the present invention. Specifically, the investigations relate to a method for managing the surface roughness of two solid bodies lubricated with a lubricant and sliding under rolling sliding conditions.

[0188] Attempts to improve tribological properties by providing characteristic shapes on surfaces have been widely conducted, and numerous reports have been published on the effects and mechanisms of various surfaces under pure sliding conditions (e.g., see Non-Patent Document 3). On the other hand, under rolling sliding conditions, although there are several reports investigating the relationship between oil film thickness and surface shape (e.g., see Non-Patent Documents 4 and 5), there are few reports on the relationship between friction and surface shape. Therefore, this paper examines a roughness management method that can meet the desired surface roughness management conditions under rolling sliding conditions when grooves are present on the surface.

[0189] [Experimental methods]

[0190] The experiments in this example used Figure 2The test was carried out using the rotating ball-and-disc tester shown in FIG. The ball and disc can be driven independently, forming a mechanism capable of performing tests at any slip rate. The friction force is determined using a torque meter attached to a shaft on the disc side. The disc test piece is made of BK7 glass, and by covering the surface with a Cr semi-transparent film and then covering it with a SiO2 film, a mechanism is formed that can measure the oil film thickness by optical interferometry (for example, see Non-Patent Document 4).

[0191] The surface roughness of the disc was Rq: 0.4 nm. For the ball test piece, a 1-inch diameter bearing steel ball (material: SUJ2) with a roughness of Rq: 5.9 nm was used, and the five groove shapes shown in Table 4 were formed parallel to the sliding direction using a picosecond laser processing machine.

[0192] Figure 17 The three-dimensional shape of the parallel grooves (the reference numeral 32 shown in the figure is a groove portion, and a flat portion 31 is formed between the groove portions 32) is shown. In addition, the test conditions are shown in Table 5. In this embodiment, Figure 17 As shown in the figure, although the parallel groove is used as the groove (groove portion) for description, the present invention is also applicable to grooves other than the parallel groove.

[0193] [Table 4]

[0194] Parallel groove shape

[0195]

[0196] [Table 5]

[0197] Experimental conditions

[0198] Temperature, °C 25 Entrainment speed, m / s 0.02 to 0.1 Slide scroll ratio, % 15 (disc > ball) Maximum contact pressure, GPa 0.34 Hertz contact radius, mm 0.12 lubricant PAO <![CDATA[Kinematic viscosity @ 40°C, mm 2 / s]]> 5.54 to 396

[0199] [Experimental results and investigation]

[0200] Figure 18 The following shows an example of the cross-sectional shape of the oil film at the center of the portion marked CL and the interference pattern measured by the optical interferometry method when using test piece A (smooth surface, test piece A, test piece C). Note that the oil film cannot be measured because light is not sufficiently reflected inside the groove. The cross-sectional shape of the oil film shows that the oil film thickness decreases locally at the groove edge and decreases overall depending on the groove area ratio. The oil film thickness hm, described later, is Figure 18 Minimum value on the central oil film section shown.

[0201] Figure 19 Indicates the friction coefficient and oil film thickness at each speed. (a) is 5.54mm 2 / s low viscosity oil results, (b) is 396mm 2 / s result of high viscosity oil.

[0202] As shown in the figure, in the case of (a) using low-viscosity oil, the friction coefficient increases as the speed decreases for all test pieces, indicating a mixed lubrication region. While there is no significant difference in oil film thickness in this lubrication region, friction increases with increasing groove area ratio, and groove depth has little effect on the friction coefficient.

[0203] On the other hand, when using fluid lubrication with high-viscosity oil, the change in oil film thickness is more significant than the change in friction. Furthermore, looking at test piece E, which has the greatest groove depth, the oil film thickness is approximately 50% of that of the smooth surface, and the friction coefficient also increases. This result differs from the results with low-viscosity oil, indicating that the influence of groove depth is greater than the influence of groove area ratio.

[0204] Figure 20 This graph shows the relationship between the actual measured oil film thickness and the friction coefficient. The oil film parameter Λ, shown on the lower horizontal axis, is calculated from hm, the composite roughness of the ball surface excluding the groove, and the disc roughness. As shown in this graph, in the mixed lubrication region (I), as described above, the friction coefficient increases with increasing area ratio.

[0205] This is because, Figure 18 As shown, the minimum oil film forms at the groove edge, so direct contact in mixed lubrication is believed to originate at the groove edge. Therefore, it is inferred that the frequency of direct contact increases when the groove area ratio is large, indicating a correlation between area ratio and friction.

[0206] On the other hand, in the fluid lubrication region (II) with an oil film thickness of approximately 100 nm (Λ = 15), the friction coefficient tends to increase slightly when the groove depth is large. In this region, since the oil film is sufficiently present, it is believed that the slight increase in friction is not due to direct contact, but rather to increased resistance due to shearing of the oil film. However, it is clear that the increase in the friction coefficient is less significant than the effect of the groove area ratio in the mixed region, and thus can be ignored.

[0207] Furthermore, it can be seen that, as in region (III), if the oil film thickness becomes large enough, the friction coefficient is the same as that of the smooth surface regardless of the groove shape. Based on the above, it can be said that the influence of the groove on friction depends not only on the groove shape but also on the lubrication state.

[0208] [in conclusion]

[0209] As described above based on the embodiments of the present invention, the results of measuring the oil film thickness and friction under rolling sliding conditions using a ball with parallel grooves revealed the following.

[0210] 1) The oil film thickness decreases locally at the groove edge. Furthermore, depending on the groove area ratio, the oil film thickness decreases not only at the groove edge but also overall.

[0211] 2) In the mixed lubrication region, friction increases as the groove area ratio increases.

[0212] 3) In the fluid lubrication area, as the groove depth increases, the friction increases slightly.

[0213] Therefore, based on the above findings, the present invention provides a surface roughness management method described in the "Problem to be Solved by the Invention." Specifically, in the surface roughness management method according to an embodiment of the present invention, oil film thickness and friction are measured under rolling sliding conditions using a ball bearing with parallel grooves. The measurement results show that the oil film thickness decreases locally at the groove edge of the parallel groove. Furthermore, depending on the groove area ratio, the oil film thickness decreases not only at the groove edge but also overall. Consequently, in the mixed lubrication region, friction increases as the parallel groove area ratio increases. Based on the above findings, the parallel groove area ratio is managed to a value below a specified value to meet the desired surface roughness management conditions. Surface roughness management conditions also include the coefficient of friction of the sliding surface and bearing torque.

[0214] Therefore, according to this surface roughness management method, by using the results of confirming the influence of the oil film thickness and friction of the parallel groove under rolling sliding conditions, the groove area ratio can be made below the specified level in a manner that satisfies the desired surface roughness management conditions.

[0215] Therefore, this surface roughness management method can provide a surface roughness management method that can meet desired surface roughness management conditions under rolling sliding conditions when parallel grooves are present on the surface. Furthermore, if this surface roughness management method is incorporated into a program, it can be applied to various devices for automatically controlling a series of steps in a workpiece grinding process, for example.

[0216] Description of Reference Signs

[0217] 1: Drive shaft; 2: Disc; 3: Ball; 4: Rotating shaft; 10: Test device; 11: Outer ring; 12: Inner ring; 13: Tapered roller; 14: Large flange; 15: Retreat groove; 20: Tapered roller bearing; 31: Flat surface; 32: Groove; A to E: Test pieces; d: Contact ellipse formed by the contact between the large flange and the end face of the roller; H: Height of the contact point between the large flange and the end face of the roller; R: Roller head radius; L: Surface pressure.

Claims

1. A friction design method for sliding parts, characterized in that: A target value for the surface roughness of the sliding surfaces of two sliding components to be managed as products is set based on the correlation between the friction coefficient obtained using a sliding surface model corresponding to the sliding surfaces of the two sliding components after lubrication with a lubricant and the oil film parameter calculated using the center level difference or the sum of the center level difference and the protruding peak height as a parameter representing the surface roughness in the sliding surface model.

2. The friction design method for sliding parts according to claim 1, wherein: According to the correlation between the friction coefficient and the oil film parameter, the target oil film parameter value corresponding to the target value is obtained. Based on the target oil film parameter value corresponding to the target value and the estimated or actually measured oil film thickness of the lubricant on the sliding surfaces of the two sliding parts, the synthetic roughness σ* of the sliding surface corresponding to the target value is calculated, thereby setting a target value for the center level difference of the surface roughness of the sliding surface to be managed as the product, or setting a target value for the sum of the center level difference of the surface roughness of the sliding surface to be managed as the product and the height of the protruding peak.

3. The friction design method for sliding parts according to claim 1 or 2, wherein: Two-dimensional roughness parameters (Rk, Rpk) are used in the center level difference and the protruding peak height.

4. The friction design method for sliding parts according to claim 1 or 2, wherein: Three-dimensional roughness parameters (Sk, Spk) are used in the center level difference and the protruding peak height.

5. A method for managing the surface roughness of a sliding component, characterized in that: A friction design method for a sliding component using any one of claims 1 to 4, The target value of the center level difference of the surface roughness of the sliding surface to be managed as the product, or the target value of the sum of the center level difference and the protruding peak height of the surface roughness of the sliding surface is used as the acceptance standard for the roughness when processing the surface of the sliding part.

6. The method for managing the surface roughness of a sliding component according to claim 5, wherein: As a pass standard for the roughness during the processing, management is also performed based on whether the value Svr satisfies the following (formula): Svr≤specified value……(formula) This value Svr represents the ratio of valleys in the surface irregularities on the sliding surface that should be managed as the product.

7. The method for managing the surface roughness of a sliding component according to claim 6, wherein: The ratio Svr of the valley portion of the surface unevenness is calculated by 100-Mr2 or 100-Rmr. Among them, Mr2 and Rmr are two-dimensional roughness parameters, Mr2 is the load length ratio of the center part of the sliding surface to be managed as the product, Rmr is the relative load length ratio of the sliding surface to be managed as the product, and the range specified by the (formula) of claim 6 is the range in which the deviation Δμ from the reference is less than a certain value.

8. The method for managing the surface roughness of a sliding component according to claim 6, wherein: The ratio Svr of the valley portion of the surface unevenness is calculated by 100-Smr2 or 100-Smr. Among them, Smr2 and Smr are three-dimensional roughness parameters, Smr2 is the load area ratio of the center part of the sliding surface to be managed as the product, Smr is the relative load area ratio of the sliding surface to be managed as the product, and the range specified by the (formula) of claim 6 is the range in which the deviation Δμ from the reference is less than a certain value.

9. The surface roughness management method according to claim 5, wherein: As a model of the sliding surface to be managed as the product, friction is measured under rolling sliding conditions using grooved balls, and based on the measurement results, the groove area ratio of the groove is managed to be below the specified level in a manner that satisfies the desired surface roughness management conditions.

10. The surface roughness management method according to claim 9, characterized in that: The grooves are parallel grooves.

11. The surface roughness management method according to claim 6, wherein: As a model of the sliding surface to be managed as the product, friction is measured under rolling sliding conditions using grooved balls, and based on the measurement results, the groove area ratio of the groove is managed to be below the specified level in a manner that satisfies the desired surface roughness management conditions.

12. The surface roughness management method according to claim 11, characterized in that: The grooves are parallel grooves.

13. A method for manufacturing a sliding mechanism, wherein the method is a method for manufacturing a sliding mechanism comprising a sliding member and a lubricant for lubricating a sliding surface of the sliding member, wherein: The sliding mechanism is manufactured using a sliding part that has been qualified by the surface roughness management method for a sliding part according to any one of claims 5 to 12.

14. The method for manufacturing a sliding mechanism according to claim 13, wherein: The sliding member is a component of a rolling bearing, a component of a sliding bearing, or a component of a ball screw.

15. The method for manufacturing a sliding mechanism according to claim 14, wherein: As the sliding component, a component is used that uses the roller head and large flange portion of a tapered roller bearing as the object, and the surface roughness of the opposing surfaces of the roller head and large flange portion is managed to be less than the surface roughness Rk or Rk+Rpk determined as the acceptance standard for roughness during processing.

16. The method for manufacturing a sliding mechanism according to claim 15, wherein: Rk+Rpk is used as a parameter for managing the surface roughness of the sliding surface of the roller head. Rk is used as a parameter for managing the surface roughness of the sliding surface of the large flange portion.

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